An Example of Blurry Boundaries

“Psychologists and psychiatrists have long tried to categorize and classify different expressions of psychopathology. The most recent addition to this endeavor is the fifth edition of the Diagnostic and Statistical Manual for Mental Disorders (DSM-5), an extensive manual describing over 150 discrete diagnoses. The DSM-5 is a reflection of the categorical model of psychopathology, in which a diagnosis reflects an underlying disorder that causes the symptoms. The manual describes specific criteria for each diagnosis. The categorical model assumes there are clear boundaries between health and pathology, and between diagnoses. This blog post is about a recent systematic review (Renard et al., 2016) in which we examined to what extent we could find these boundaries between schizophrenia spectrum disorders (or schizophrenias) and dissociative disorders.

“The DSM-5 is a reflection of the categorical model of psychopathology [which] assumes there are clear boundaries between health and pathology, and between diagnoses”

According to the DSM-5, a typical schizophrenia spectrum disorder patient perceives things that are not there (i.e., has hallucinations), holds beliefs that do not match reality (i.e., has delusions), is hard to follow, and/or withdraws from society (i.e., has negative symptoms). In contrast, a typical dissociative disorder patient would in the past have been described as someone with multiple personalities. Problems with integrating different parts of one’s personality constitutes the most severe form of dissociation. Dissociation also includes difficulties with integrating thoughts, feelings, and memories. The two diagnoses are also commonly believed to differ in what causes them. Schizophrenias are generally thought to be primarily caused by biological factors, whereas dissociative disorders are believed to be caused by severe trauma.

Despite the clear distinction made in the DSM-5, the literature shows a far more muddled picture. Up to 50% of the patients diagnosed with one of the disorders also meet the diagnostic criteria for the other disorder. Moreover, most of the symptoms typically associated with one of the two diagnostic groups are also, to a certain extent, seen in the other diagnostic group. For example, there is a large body of evidence showing that dissociative symptoms, such as feeling like a stranger to oneself, are more common in patients with schizophrenia than in healthy controls, albeit less so than in patients with a dissociative disorder. While there is less research on the prevalence of symptoms typically associated with schizophrenias in patients with a dissociative disorder, the available data indicate that hallucinations, delusions, and negative symptoms are also reported by patients with a dissociative disorder.

“[Schizophrenia spectrum disorders and dissociative disorders] are not as distinct as the DSM-5 makes them out to be”

The overlap between these disorders goes beyond their symptoms; with regard to what causes the different problems, the boundaries are similarly unclear. This is partly because there is no consensus about the exact cause for both diagnostic groups. While schizophrenias have a genetic component and have often been associated with altered functioning of certain brain areas, they are also thought to have environmental causes, such as trauma. Similarly, there is evidence that dissociative disorders are not only related to trauma but also to suggestibility and fantasy proneness, two personality characteristics that are also common in patients with a schizophrenia spectrum disorder. Furthermore, dissociative disorders and schizophrenias have been related to similar alterations in the functioning of specific brain areas.

To sum up, it seems like these disorders are not as distinct as the DSM-5 makes them out to be. Indeed, instead of seeing symptoms as being caused by categorically distinct underlying disorders, these results fit a lot better with the so-called dimensional model of psychopathology. This model states that the symptoms experienced by people with a certain diagnosis are more severe but otherwise similar to the experiences people without this diagnosis may have, be it non-patients or patients with a different diagnosis. For example, when someone diagnosed with schizophrenia is said to have persecutory delusions, this means he is extremely suspicious, an experience similar to how other people might experience suspicions. In other words, according to the dimensional model of psychopathology, to a certain extent we all have these experiences.

“While categorical diagnoses might seem appealing as a common language in a complex field, the question is whether this simplification solves more problems than it creates. “

The blurry boundaries between diagnoses can further be explained by the network model of psychopathology. According to this model, symptoms are not necessarily the result of underlying disorders but can be caused by other symptoms. For example, there are indications that people who feel detached from everyday experiences (i.e., experience dissociation) can start to have difficulty in distinguishing what is real from what is not. This impaired reality testing can, in turn, lead to hallucinations and delusions. In other words, a diagnosis reflects a network of interacting symptoms. Importantly the links between symptoms might differ from individual to individual: for some individuals dissociation might lead to hearing things, while for others it might lead to withdrawal.

While categorical diagnoses might seem appealing as a common language in a complex field, the question is whether this simplification solves more problems than it creates. If the benefits don’t outweigh the costs, we should change the language. In practice it is important to realize that psychological problems do not have clear diagnostic boundaries. While a diagnosis might be useful in pointing towards a certain treatment approach, the exact treatment should be adjusted to the individual. For example, someone diagnosed with schizophrenia who also has dissociative symptoms should be helped with the dissociative problems, regardless of the diagnosis.

Selwyn Renard is a PhD candidate in Clinical Psychology and Experimental Psychopathology at the University of Groningen. Here he previously graduated from the Psychology Bachelor program and the Behavioural and Social Sciences Research Master program. He enjoys asking difficult questions and equally enjoys finding answers to those questions. During his education he got intrigued with psychopathology, phenomenology, differential diagnosis in general, and in particular differential diagnosis concerning schizophrenia spectrum disorders and dissociative disorders. Together with Dr. Marieke Pijnenborg, Dr. Rafaele Huntjens, and Prof. André Aleman he obtained funding for his PhD project, Psychotic disorders And Dissociation (PAD), in which he tries to unravel the exact relationship between schizophrenia spectrum disorders and dissociative disorders. Currently Selwyn is in the final year of his PhD program, focusing on finishing his project and writing his dissertation.